Cell culture assay systems will be utilized to determine toxicity and carcinogenicity of several PCB congeners including dichlorobiphenyls, tetrachlorobiphenyls, pentachlorobiphenyls, and hexachlorobiphenyls. Metabolic products produced by the fibroblast cell line and hepatocytes will be isolated and identified. Ultrastructural characterization of the transformed cells will be performed. Rats exposed to 100 ppm hexachlorobiphenyl or Aroclor 1260 in the diet will be evaluated for hepatic lesions, particularly the formation of neoplasms. The ultrastructural features of the lesions will be characterized. Metabolites of hexachlorobiphenyls produced by the liver of rhesus monkeys and excreted in the bile will be isolated and identified.